1. Field of the Invention
This invention relates generally to a method and apparatus for the control of oil and gas production wells. More particularly, this invention relates to a method and apparatus for automatically controlling petroleum production wells using downhole computerized control systems. This invention also relates to a control system for controlling production wells, including multiple zones within a single well, from a remote location.
2. The Prior Art
The control of oil and gas production wells constitutes an on-going concern of the petroleum industry due, in part, to the enormous monetary expense involved as well as the risks associated with environmental and safety issues.
Production well control has become particularly important and more complex in view of the industry wide recognition that wells having multiple branches (i.e., multilateral wells) will be increasingly important and commonplace. Such multilateral wells include discrete production zones which produce fluid in either common or discrete production tubing. In either case, there is a need for controlling zone production, isolating specific zones and otherwise monitoring each zone in a particular well.
Before describing the current state-of-the-art relative to such production well control systems and methods, a brief description will be made of the production systems, per se, in need of control. One type of production system utilizes electrical submersible pumps (ESP) for pumping fluids from downhole. In addition, there are two other general types of productions systems for oil and gas wells, namely plunger lift and gas lift. Plunger lift production systems include the use of a small cylindrical plunger which travels through tubing extending from a location adjacent the producing formation down in the borehole to surface equipment located at the open end of the borehole. In general, fluids which collect in the borehole and inhibit the flow of fluids out of the formation and into the wellbore, are collected in the tubing. Periodically, the end of the tubing is opened at the surface and the accumulated reservoir pressure is sufficient to force the plunger up the tubing. The plunger carries with it to the surface a load of accumulated fluids which are ejected out the top of the well thereby allowing gas to flow more freely from the formation into the wellbore and be delivered to a distribution system at the surface. After the flow of gas has again become restricted due to the further accumulation of fluids downhole, a valve in the tubing at the surface of the well is closed so that the plunger then falls back down the tubing and is ready to lift another load of fluids to the surface upon the reopening of the valve.
A gas lift production system includes a valve system for controlling the injection of pressurized gas from a source external to the well, such as another gas well or a compressor, into the borehole. The increased pressure from the injected gas forces accumulated formation fluids up a central tubing extending along the borehole to remove the fluids and restore the free flow of gas and/or oil from the formation into the well. In wells where liquid fall back is a problem during gas lift, plunger lift may be combined with gas lift to improve efficiency.
In both plunger lift and gas lift production systems, there is a requirement for the periodic operation of a motor valve at the surface of the wellhead to control either the flow of fluids from the well or the flow of injection gas into the well to assist in the production of gas and liquids from the well. These motor valves are conventionally controlled by timing mechanisms and are programmed in accordance with principles of reservoir engineering which determine the length of time that a well should be either xe2x80x9cshut inxe2x80x9d and restricted from the flowing of gas or liquids to the surface and the time the well should be xe2x80x9copenedxe2x80x9d to freely produce. Generally, the criteria used for operation of the motor valve is strictly one of the elapse of a preselected time period. In most cases, measured well parameters, such as pressure, temperature, etc. are used only to override the timing cycle in special conditions.
It will be appreciated that relatively simple, timed intermittent operation of motor valves and the like is often not adequate to control either outflow from the well or gas injection to the well so as to optimize well production. As a consequence, sophisticated computerized controllers have been positioned at the surface of production wells for control of downhole devices such as the motor valves.
In addition, such computerized controllers have been used to control other downhole devices such as hydro-mechanical safety valves. These typically microprocessor based controllers are also used for zone control within a well and, for example, can be used to actuate sliding sleeves or packers by the transmission of a surface command to downhole microprocessor controllers and/or electromechanical control devices.
The surface controllers are often hardwired to downhole sensors which transmit information to the surface such as pressure, temperature and flow. This data is then processed at the surface by the computerized control system. Electrically submersible pumps use pressure and temperature readings received at the surface from downhole sensors to change the speed of the pump in the borehole. As an alternative to downhole sensors, wire line production logging tools are also used to provide downhole data on pressure, temperature, flow, gamma ray and pulse neutron using a wire line surface unit. This data is then used for control of the production well.
There are numerous prior art patents related to the control of oil and gas production wells. In general, these prior patents relate to (1) surface control systems using a surface microprocessor and (2) downhole control systems which are initiated by surface control signals.
The surface control system patents generally disclose computerized systems for monitoring and controlling a gas/oil production well whereby the control electronics is located at the surface and communicates with sensors and electromechanical devices near the surface. An example of a system of this type is described in U.S. Pat. No. 4,633,954 (""954) to Dixon et al. The system described in the ""954 patent includes a fully programmable microprocessor controller which monitors downhole parameters such as pressure and flow and controls the operation of gas injection to the well, outflow of fluids from the well or shutting in of the well to maximize output of the well. This particular system includes battery powered solid state circuitry comprising a keyboard, a programmable memory, a microprocessor, control circuitry and a liquid crystal display. Another example of a control system of this type is described in U.S. Pat. No. 5,132,904 (""904) to Lamp. The ""904 patent discloses a system similar to the ""954 patent and in addition also describes a feature wherein the controller includes serial and parallel communication ports through which all communications to and from the controller pass. Hand held devices or portable computers capable of serial communication may access the controller. A telephone modem or telemetry link to a central host computer may also be used to permit several controllers to be accessed remotely.
U.S. Pat. No. 4,757,314 (""314) to Aubin et al describes an apparatus for controlling and monitoring a well head submerged in water. This system includes a plurality of sensors, a plurality of electromechanical valves and an electronic control system which communicates with the sensors and valves. The electronic control system is positioned in a water tight enclosure and the water tight enclosure is submerged underwater. The electronics located in the submerged enclosure control and operate the electromechanical valves based on input from the sensors. In particular, the electronics in the enclosure uses the decision making abilities of the microprocessor to monitor the cable integrity from the surface to the well head to automatically open or close the valves should a break in the line occur.
The downhole control system patents generally disclose downhole microprocessor controllers, electromechanical control devices and sensors. Examples include U.S. Pat. Nos. 4,915,168 (""168) to Upchurch and 5,273,112 (""112) to Schultz. However, in each and every case, the microprocessor controllers transmit control signals only upon actuation from a surface or other external control signal. There is no teaching in any of these patents that the downhole microprocessor controllers themselves may automatically initiate the control of the electromechanical devices based on preprogrammed instructions. Similarly, none of the aforementioned patents directed to microprocessor based control systems for controlling the production from oil and gas wells, including the aforementioned ""954, ""904 and ""314 patents, disclose the use of downhole electronic controllers, electromechanical control devices and sensors whereby the electronic control units will automatically control the electromechanical devices based on input from the sensor without the need for a surface or other external control signal.
It will be appreciated that the downhole control system of the types disclosed in the ""168 and ""112 patents are closely analogous to the surface based control systems such as disclosed in the ""954, ""904 and ""314 patents in that a surface controller is required at each well to initiate and transmit the control instructions to the downhole microprocessor. Thus, in all cases, some type of surface controller and associated support platform at each well is needed.
While it is well recognized that petroleum production wells will have increased production efficiencies and lower operating costs if surface computer based controllers and downhole microprocessor controller (actuated by external or surface signals) of the type discussed hereinabove are used, the presently implemented control systems nevertheless suffer from drawbacks and disadvantages. For example, as mentioned, all of these prior art systems generally require a surface platform at each well for supporting the control electronics and associated equipment. However, in many instances, the well operator would rather forego building and maintaining the costly platform. Thus, a problem is encountered in that use of present surface controllers require the presence of a location for the control system, namely the platform. Still another problem associated with known surface control systems such as the type disclosed in the ""168 and ""112 patents wherein a downhole microprocessor is actuated by a surface signal is the reliability of surface to downhole signal integrity. It will be appreciated that should the surface signal be in any way compromised on its way downhole, then important control operations (such as preventing water from flowing into the production tubing) will not take place as needed.
In multilateral wells where multiple zones are controlled by a single surface control system, an inherent risk is that if the surface control system fails or otherwise shuts down, then all of the downhole tools and other production equipment in each separate zone will similarly shut down leading to a large loss in production and, of course, a loss in revenue.
Still another significant drawback of present production well control systems involves the extremely high cost associated with implementing changes in well control and related workover operations. Presently, if a problem is detected at the well, the customer is required to send a rig to the well site at an extremely high cost (e.g., 5 million dollars for 30 days of offshore work). The well must then be shut in during the workover causing a large loss in revenues (e.g., 1.5 million dollars for a 30 day period). Associated with these high costs are the relatively high risks of adverse environmental impact due to spills and other accidents as well as potential liability of personnel at the rig site. Of course, these risks can lead to even further costs. Because of the high costs and risks involved, in general, a customer may delay important and necessary workover of a single well until other wells in that area encounter problems. This delay may cause the production of the well to decrease or be shut in until the rig is brought in.
Still other problems associated with present production well control systems involve the need for wireline formation evaluation to sense changes in the formation and fluid composition. Unfortunately, such wireline formation evaluation is extremely expensive and time consuming. In addition, it requires shut-in of the well and does not provide xe2x80x9creal timexe2x80x9d information. The need for real time information regarding the formation and fluid is especially acute in evaluating undesirable water flow into the production fluids.
U.S. Pat. No. 5,531,270 discloses remotely controllable fluid flow control valves disposed in the main wellbore and branch wellbores of a multiple well. Each flow control valve has a radio frequency range receiver, a controller and an actuator for moving a closure member to a selected position to control fluid flow in the wellbore in which the valve is disposed. A signal transmitter is conveyed into the main wellbore by a line or coilable tubing and radio frequency range electromagnetic wave energy signals are transmitted to the selected valve to effect fluid flow control within each wellbore of the multiple well.
However, fluid flow conditions for a particular wellbore can only be monitored when the transmitter is placed in proximity to the fluid flow control valve to be controlled. This wireline (or coil tubing) device suffers from the same aforementioned problem and deficiencies of other wireline devices.
The above-discussed and other problems and deficiencies of the prior art are overcome or alleviated by the production well control system of the present invention. In accordance with the present invention, a downhole production well control system is provided for automatically controlling downhole tools in response to sensed selected downhole parameters. An important feature of this invention is that the automatic control is initiated downhole without an initial control signal from the surface or from some other external source.
The present invention generally comprises downhole sensors, downhole electromechanical devices and downhole computerized control electronics whereby the control electronics automatically control the electromechanical devices based on input from the downhole sensors. Thus, using the downhole sensors, the downhole computerized control system will monitor actual downhole parameters (such as pressure, temperature, flow, gas influx, etc.) and automatically execute control instructions when the monitored downhole parameters are outside a selected operating range (e.g., indicating an unsafe condition). The automatic control instructions will then cause an electromechanical control device (such as a valve) to actuate a suitable tool (for example, actuate a sliding sleeve or packer; or close a pump or other fluid flow device).
The downhole control system of this invention also includes transceivers for two-way communication with the surface as well as a telemetry device for communicating from the surface of the production well to a remote location.
The downhole control system is preferably located in each zone of a well such that a plurality of wells associated with one or more platforms will have a plurality of downhole control systems, one for each zone in each well. The downhole control systems have the ability to communicate with other downhole control systems in other zones in the same or different wells. In addition, as discussed in more detail hereinafter, each downhole control system in a zone may also communicate with a surface control system. The downhole control system of this invention thus is extremely well suited for use in connection with multilateral wells which include multiple zones.
The selected operating range for each tool controlled by the downhole control system of this invention is programmed in a downhole memory either before or after the control system is lowered downhole. The aforementioned transceiver may be used to change the operating range or alter the programming of the control system from the surface of the well or from a remote location.
A power source provides energy to the downhole control system. Power for the power source can be generated in the borehole (e.g., by a turbine generator), at the surface or be supplied by energy storage devices such as batteries (or a combination of one or more of these power sources). The power source provides electrical voltage and current to the downhole electronics, electromechanical devices and sensors in the borehole.
In contrast to the aforementioned prior art well control systems which consist either of computer systems located wholly at the surface or downhole computer systems which require an external (e.g., surface) initiation signal (as well as a surface control system), the downhole well production control system of this invention automatically operates based on downhole conditions sensed in real time without the need for a surface or other external signal. This important feature constitutes a significant advance in the field of production well control. For example, use of the downhole control system of this invention obviates the need for a surface platform (although such surface platforms may still be desirable in certain applications such as when a remote monitoring and control facility is desired as discussed below). The downhole control system of this invention is also inherently more reliable since no surface to downhole actuation signal is required and the associated risk that such an actuation signal will be compromised is therefore rendered moot. With regard to multilateral (i.e., multi-zone) wells, still another advantage of this invention is that, because the entire production well and its multiple zones are not controlled by a single surface controller, then the risk that an entire well including all of its discrete production zones will be shut-in simultaneously is greatly reduced.
Further, a system adapted for controlling and/or monitoring a plurality of production wells from a remote location is provided. This system is capable of controlling and/or monitoring:
(1) a plurality of zones in a single production well;
(2) a plurality of zones/wells in a single location (e.g., a single platform); or
(3) a plurality of zones/wells located at a plurality of locations (e.g., multiple platforms).
The multizone and/or multiwell control system of this invention is composed of multiple downhole electronically controlled electromechanical devices (sometimes referred to as downhole modules), and multiple computer based surface systems operated from multiple locations. Important functions for these systems include the ability to predict the future flow profile of multiple wells and to monitor and control the fluid or gas flow from either the formation into the wellbore, or from the wellbore to the surface. The control system of this invention is also capable of receiving and transmitting data from multiple remote locations such as inside the borehole, to or from other platforms, or from a location away from any well site.
The downhole control devices interface to the surface system using either a wireless communication system or through an electrical hard wired connection. The downhole control systems in the wellbore can transmit and receive data and/or commands to/from the surface system. The data transmission from inside the wellbore can be done by allowing the surface system to poll each individual device in the hole, although individual devices will be allowed to take control of the communications during an emergency. The devices downhole may be programmed while in the wellbore by sending the proper command and data to adjust the parameters being monitored due to changes in borehole and flow conditions and/or to change its primary function in the wellbore.
The surface system may control the activities of the downhole modules by requesting data on a periodic basis, and commanding the modules to open or close the electromechanical control devices, and/or change monitoring parameters due to changes in long term borehole conditions. The surface system at one location will be capable of interfacing with a system in another location via phone lines, satellite communication or other communicating means. Preferably, a remote central control system controls and/or monitors all of the zones, wells and/or platforms from a single remote location.
In accordance with another embodiment of the present invention, the downhole control systems are associated with permanent downhole formation evaluation sensors which remain downhole throughout production operations. These formation evaluation sensors for formation measurements may include, for example, gamma ray detection for formation evaluation, neutron porosity, resistivity, acoustic sensors and pulse neutron which can, in real time, sense and evaluate formation parameters including important information regarding water migrating from different zones. Significantly, this information can be obtained prior to the water actually entering the producing tubing and therefore corrective action (i.e., closing of a valve or sliding sleeve) or formation treatment can be taken prior to water being produced. This real time acquisition of formation data in the production well constitutes an important advance over current wireline techniques in that the present invention is far less costly and can anticipate and react to potential problems before they occur. In addition, the formation evaluation sensors themselves can be placed much closer to the actual formation (i.e., adjacent the casing or downhole completion tool) then wireline devices which are restricted to the interior of the production tubing.
In accordance with the present invention, a completed well having a production tubing string therein with multiple branches, i.e., zones, communicates and transmitts power over a combination of a hardwire system in the main borehole and a short hop system in the branches or laterals. The production tubing string in the main borehole includes packers located uphole and downhole from each of the zones. Each zone includes a downhole control system and appropriate completion devices for controling fluid flow.
An acoustic or electromagnetic transciever is associated with each control system for communication and/or transmission of power. An electrical conductor runs from the surface downhole along the production tubing string in the main borehole for communication and/or transmission of power, hardwired systems are well known. The conductor is connected to an acoustic or electromagnetic transceiver disposed at the production tubing string in the main borehole near each branch. These transceivers communicate with and/or transfer power to corresponding transceivers at the branches (i.e., short hop communications), which is communicated and/or transferred along the production tubing string on the conductor (i.e., uphole or downhole).
With acoustic transceivers (transmitter and/or receiver) acoustic or seismic signals travel through the production string or the earth. With electromagnetic transceivers (transmitter and/or receiver) electromagnetic (xe2x80x9cEMxe2x80x9d) waves through the production string and the earth. Typically, a pickup assembly or loop antenna (e.g. a toriod) is located around the production tubing string. These signals are only required to travel a short distance, whereby the large power requirement systems designed for transmission over long distances (several thousand feet) are not required.
Communication and/or transmission of power along the laterals can be accomplished, by way of, a hardwire, acoustic transmission, electromagnetic transmission or any other suitable method.
The above-discussed and other features and advantages of the present invention will be appreciated by and understood by those skilled in the art from the following detailed description and drawings.